1. Field of the Disclosure
The present disclosure relates to a method for reclaiming a surface of a substrate. In particular, the present disclosure relates to a method for reclaiming a surface of a silicon substrate that includes a protruding residual topography resulting from a layer transfer process typically comprising an ion implantation step, a bonding step and a detachment step.
2. Description of Related Art
The so-called Smart Cut™ process, illustrated in FIG. 1, provides high quality silicon on insulator (SOI) substrates. During this process, two substrates, called a handle substrate 101 and a donor substrate 103, usually a silicon wafer, undergo a certain number of process steps to transfer a layer with a given thickness of the donor substrate 103 onto the handle substrate 101. During the process, the donor substrate 103 is typically oxidized to form an oxidation layer 105, which later forms the buried oxide layer (BOX) of the SOI structure, and an ion implantation step is applied to form a predetermined splitting area 107 defining the layer that is to be transferred. Subsequently, the donor substrate 103 is attached to the handle substrate 101, in particular via bonding, taking advantage of Van der Waal's forces, to obtain a donor-handle compound 109. Using a mechanical and/or thermal treatment, a detachment of a semiconductor layer 111 together with the buried oxide layer 113 occurs at the predetermined splitting area 107 so that the two layers are transferred onto the handle substrate 101 to obtain the desired silicon on insulator structure 115.
The remaining part 117 of the donor substrate 101, also called the negative, can be recycled and again used in the Smart Cut™ type process as a new donor or handle substrate. This recycling aspect of the Smart Cut™ type SOI fabrication process provides a significant economic advantage when compared with other processes. Indeed, the process optimizes the use of raw materials such as silicon wafers.
As illustrated in FIG. 1, the negative 117 has a characteristic topography representing protruding residues 119a and 119b in an edge region, which corresponds to a region where no layer transfer occurred due to the shape of the edge of the initial wafers 103 and/or 101. The surface of the negative 117 between the protruding residues 119a and 119b has a first inner region 121 at which detachment occurred to provide the transferred layer 111 on the handle substrate 101 and which has a rather rough surface typically close to 60-70 angstrom (Å) RMS as measured by atomic force microscopy (AFM), which is to be compared to 1-3 Å for a standard silicon wafer. The edge of the negative 117 with the protruding residues 119a and 119b actually has a chamfered shape and furthermore comprises a step-like structure 123 seen from the internal region 121 comprising the remaining part of the buried oxide layer 125 and the non-transferred silicon 127 over the remaining part of the ion implanted predetermined splitting area 129. The edge 131 and the backside 133 of the negative 117 are also covered by the oxide.
The step-like structure 123 of the negative 117 typically has a thickness of about 1000-10000 Å of silicon, mostly between 2000 to 3000 Å, 100 to 10000 Å of silicon oxide and has a width w in the lateral direction on the order of 1-3 mm.
Prior to the reuse of the negative 117 as donor substrate 103 or handle substrate 101, the surface roughness of the inner region 121 needs to be reduced and the protruding residual topography 119a and 119b need to be removed. Methods to do so are, for example, known from EP 1 156 531 A1 and U.S. Pat. No. 7,402,520 B2. Typically, the following process is applied to get rid of the protruding residual topography: the reclaiming process starts with a de-oxidation step to remove the oxide layer 125 on top of the protruding residual topography on the edge of the negative 117 as well as on the side 131 and on its backside 133. The de-oxidation can, for example, be carried out using a hydrofluoric acid (HF) bath, wherein the acid consumes the oxide layer 125, 131 and 133. Subsequently, a first polishing step of the edge region of substrate 1 is carried out to at least partially remove the protruding silicon part 127 on the edge. Then a double-sided polishing (DSP) step is carried out to improve the surface roughness in the interior region 121 but also to further remove the step 123 in the direction of the protruding residual topography 119a and 119b. Finally, to obtain a suitable surface roughness on the front surface of the negative 117, a chemical mechanical polishing step (CMP) is carried out.
Even though it is possible to obtain a recycled substrate that can be reused in the Smart Cut™ process using the reclaiming process described above, this process includes a double-sided polishing step, which has the major disadvantage that, during polishing, up to 10 μm (5 μm on each side of the substrate) must be removed to get rid of the protruding residual topography 119a and 119b. Therefore, it is an object of the present disclosure to provide an improved reclaiming process that does not require the double-sided polishing step to reclaim the remainder of the donor substrate.